RISSOA. 9 



15 on the penultimate, 14 on the succeeding whorl, and 13 on 

 the next, not more than half the last number being discernible 

 on the upper whorl, when they altogether disappear ; these 

 ribs are continued to the base, which is furnished with an an- 

 gular projection or knob, owing to this part of the pillar being 

 greatly thickened ; there are also equally strong spiral ribs, 6 

 of which are on the body- whorl, 3 or 4 on the penultimate, 

 and 2 only on each of the succeeding three whorls ; the first 

 two or three whorls are apparently quite smooth and glossy, but 

 under the microscope exhibit extremely fine and numerous 

 longitudinal wavy striae ; the two sets of ribs cross each other, 

 leaving between them square cavities and forming at the points 

 of intersection raised and rather sharp tubercles, imparting to 

 the surface a- prickly aspect; labial rib broad, and traversed 

 by the spiral ribs up to the mouth, the edge of which conse- 

 quently becomes scalloped or indented : colour yellowish-white, 

 with often more or less of a rufous tinge, or indistinctly marked 

 by two reddish -brown bands, a narrow one below the suture 

 and a broad one round the periphery ; sometimes the colour is 

 milk-white ; the throat or inside of the mouth is frequently 

 stained by reddish-brown : spire short and acute : whorls 6-7, 

 convex, the last occupying two-thirds of the total length ; the 

 first two or three whorls are disproportionately small : suture 

 broadly excavated : mouth roundish oval, expanding outwards, 

 finely and closely ridged lengthwise on the inside of the labial 

 rib ; there are 12 of these ridges, besides usually a blunt 

 tubercle on the lower part of the pillar : outer lip thin : inner 

 lip forming a rather broad glaze on the pillar, which is imper- 

 forate : operculum not very thin, having a somewhat lateral 

 spire (as in Littorina), and conspicuously and closely striated 

 in a curved direction corresponding with the line of growth. 

 L. 0-185. B. 0-115. 



Yar. paupercula. Dwarfed, more regularly oval and solid, 

 with a proportionally longer spire. L. 0-135. B. 0*005. 



Habitat : Rocks and stones at low water of spring- 

 tides, and the coralline zone, in the Channel Isles and 

 on many parts of the Cornish coast ; rather common, 

 especially at Herm. Received from Sandwich (Mon- 

 tagu) ; west bay of Portland, 15 f. (M f Andrew and 

 Forbes) ; Torquay (Hanley) ; Salcombe Bay (Barlee) j 



B O 



